I've been a landlord since 1980, so some experience of the good, the bad and the ugly tenant.
I have a number of house 'rules,' some of which are not very nice, but it's decades of experience that have built them up.
Rule 1. I always use an agent to find my tenants, they will charge me about 12% for the task, so about one months rent, I consider this money well spent, I would not even consider sites such as Gumtree, although I might consider some of the on-line agents in future
I give the agents a list of my likes and dislikes for the particular property, as a blanket rule, no DSS, no Students, no council tenants, no multiple sharers, no pets, no smokers, and before anyone says anything about those exclusions, the vast majority of Buy To Let mortgages have those conditions before they will give a landlord a loan.
Due to the Conservative Governments latest law, which makes landlords responsible for illegal immigrants, I will only accept EU and Scandinavian passports. Don't bother applying if you don't have one.
Once they have got past those minimum requirements, and they like the flat, then we go for the full credit check, bank statements, salary statements, tax statements, previous landlord (and I phone them up), and work statements ( and I call them as well) if, as has happened, companies will not provide details of their staff, then the staff do not get the property.
(I tell them why, and cc the company)
It may all sound a bit over the top, but if you are lending an asset worth over quarter of a million quid to someone, you need to know exactly who they are. Any doubts, then find another tenant, it's a landlords market.
As a minimum, I always change a six week deposit, and if I could get 3 months (which is normal elsewhere in Europe ) then I would. I protect all my own deposits.
That all said, in 35 years of doing this, I've only had to take one tenant to court, I've had a few bad ones, a couple of ugly ones and many dozens of really good ones, some of whom have stayed for years and years, and even some who have come back a decade later.
I've been invited to tenants weddings bar mitzvahs, and funerals, I still keep in touch with tenants of 30 years ago, and I have provided them references for other landlords and house purchases,